1. Field of the Invention
The present invention relates to the novel copolymers of sulfur dioxide and trialkylgermylstyrene and more particularly, to copolymers exhibiting a high sensitivity to light, electron beam, and X-ray, as well as having an excellent dry etching resistance, and their application as positive resist material.
2. Description of the Prior Art
Recent developments in LSI (Large Scale Integration) have resulted in a demand for a high performance of a high sensitivity, a submicron resolution, and dry etching resistance in their application as a positive resist material. In general, most of main chain scission type positive resist materials exhibit an internal conflict relationship between a sensitivity and an anti-dry etching resistance. That is, the higher the sensitivity of positive resist material, the lower its dry etching resistance. For example, a conventional high positive resist material exhibiting a high sensitivity is a copolymer of sulfur dioxide and olefin (M. J. Bowden and L. F. Thompson, J. Electrochem. Soc., 120, 1722, 1973). Poly(1-butene sulfone) of the copolymer of sulfur dioxide and olefin has a high sensitivity and a low dry etching resistance during electron beam irradiation. In order to give dry etching resistance characteristics to poly (olefin sulfone), a unit having an aromatic ring such as styrene is included in the poly (olefin sulfone) unit. In the prior art, when the ratio of styrene and sulfur dioxide is more than 2 in the copolymer, the resulting poly (styrene sulfone), ##STR1## is soluble in a solvent. However, this prior art copolymer exhibits a high dry etching resistance and a poor sensitivity (M. J. Bowden and L. F. Thompson, J. Electrochem. Soc., 121, 1620, 1974).